Danger of electrocution from ungrounded system

[dfdt]

Just wondering what will happen if one inadverently comes in contact with one phase of 22kV feeder conductor fed via ungrounded source? I have read that such a system will sustain fault current due to phase to ground capacitances[highlight ][/highlight] of healthy phases.Could this capacitive current be fatal? Please share your views.

 

[Marmite]

Yes it could be fatal. You would only need a few tens of milliamps to flow through a body to cause ventricular fibrillation.
Regards
Marmite

 

[ScottyUK]

Concur with Marmite - very probably fatal.

 

[dfdt]

Thanks guys for sharing your views

 

[Mbrooke]

The current might not be enough to cause arc blast, but it is a few amps on average. More then enough to harm.

 

[electricallearn]

Does this mean that all ungrounded systems will need a voltage based protection for safety of personnel, if the damaged part, say for instance HV cable on a cable ladder is accessible to personnel?

 

[mard57]

If the system is ungrounded, fault current will be based on capacitive coupling between ground and the ungrounded neutral. The capacitance will determine the amplitude of L-G fault current. A low capacitance value will result in higher capacitive reactance Xc = 1/jwc. Therefore it will result in a lower L-G fault current amplitude.

If you touch the faulted conductor, then the current amplitude between you and ground will be based on your bodies impedance to ground relative to the faulted conductor's impedance to ground (in parallel) and unrelated to the capacitance from ground - neutral which is in series. Both current amplitudes (conductor - human - ground and conductor directly to ground) are affected by the same capacitance.

 

[7anoter4]

In my opinion, it depends on supply cable length , transformer rated power and the ground fault protection clearing time.
For instance, for small transformer[100 kva] and short supply cable[10 ft] a 50 kg human body will be damaged in less than 1 minute.
For large transformer[1000 kVA] and medium supply cable length[1000 ft] the 50 kg body will be damaged in less than 0.1 seconds.

 

[FPelec]

Most probably it is fatal.
Here where I live the 20 kV system neutral is compensated using Petersen coil, so that the earth fault current is very low: nonetheless most accidents on that lines are fatal (

http://www.corriere.it/cronache/12_...a_8ece40b2-38d9-11e2-a2c7-8d9940659020.shtml)

Si duri puer ingeni videtur,
preconem facias vel architectum.